There is known a variable valve operating mechanism or valve train provided with cam carriers having thereon plural cam lobes different in cam profile for determining valve operating characteristics. The cam carriers are axially slidably fitted on camshafts, respectively, in such a state that rotation of the cam carriers relative to the camshafts is prevented and that axial shift of the cam carriers causes different cam lobes to act on engine valves to change the valve operating characteristics (for example, refer to Patent Document 1).